Neurochemical correlates of behavior: levels of amino acids in four areas of the brain of the rat during drug-induced behavioral excitation.

The levels of GABA, aspartate, glutamate, glycine and alanine were determined in 4 specific brain areas (telencephalon, diencephalon-mesencephalon cerebellum and pons-medulla oblongata) of rats killed during a period of drug-induced behavioral excitation. Behavioral excitation was obtained in adult, male Wistar rats working on a Sidman shock-avoidance schedule following administration of 2 mg/kg tetrabenazine (TBZ) 18 hr after iproniazid (50 mg/kg) pretreatment. When compared to trained animals (working on the avoidance schedule but receiving no drugs), the excited rats had increased levels of GABA in the telencephalon and diencephalon-mesencephalon, decreased levels of aspartate in all 4 brain areas, and a lower content of glycine in the pons-medulla region. The changes in the levels of aspartate in all areas of the brain, GABA in the diencephalon-mesencephalon, and glycine in the pons-medulla were significantly correlated (p less than 0.01) with the degree of excitation. It was observed that avoidance training alone produced increases in the levels of four amino acids: aspartate in telencephalon and cerebellum, GABA in cerebellum, and glycine and glutamate in the pons-medulla. The injection of iproniazid alone or iproniazid followed by TBZ into naive animals had little effect on the levels of the five amino acids. The data are discussed in terms of aspartate and GABA interacting as neurotransmitters with cholinergic and catecholaminergic and/or serotonergic neurons to produced the behavioral excitation.